text: In magnetic spectroscopy (EPR, NMR), a microwave pulse (EPR) or a radio frequency pulse (NMR) in a strong ambient magnetic field is used as the energizing event.  This turns the magnetic particles at an angle to the ambient field, resulting in gyration.  The gyrating spins then induce a periodic current in a detector coil.  Each spin exhibits a characteristic frequency of gyration (relative to the field strength) which reveals information about the analyte.
  In Fourier-transform mass spectrometry, the energizing event is the injection of the charged sample into the strong electromagnetic field of a cyclotron.  These particles travel in circles, inducing a current in a fixed coil on one point in their circle.  Each traveling particle exhibits a characteristic cyclotron frequency-field ratio revealing the masses in the sample.